How do I turn off the three note chime when entering PIN?

[alexp78]

When turning the Moto G on, there is a loud three note chime just after entering the PIN.
How to stop this?
It has always been there, since KitKat and still there now upgraded to 5.1.

I have been to:
Settings > Sound and Notification > Other Sounds > Screen locking sounds
and turned this off.

Thanks.